Recent studies in mice, nonhuman primates, and clinical trials in human patients have emphasized the importance of the persistence of the vaccine-induced immune response, immunological memory, in mediating protective immunity against infectious diseases and cancer. Notably, inhibition of mediators of effector differentiatio like mTOR, GSK3b, Blimp-1 or T-bet, using genetic means or whenever available pharmacological agents, not only prevented the accumulation of the short-lived effectors but also redirected the activated T cells to differentiate along the memory pathway, and potentiated vaccine-induced protective immunity in mice. Notwithstanding, pharmacological agents, like rapamycin that was used to inhibit mTOR, often exhibit undesirable immune suppressive effects reflecting the broad distribution of their targets. Here we propose to develop a versatile, broadly applicable, and clinically feasible approach to promote the generation of memory T cell responses that addresses the main limitations of pharmacological agents. We propose to use RNAi to downregulate intracellular mediators of effector differentiation that will be targeted to CD8+ T cells by conjugation to oligonucleotide aptamer ligands. Aptamer and aptamer-siRNA conjugates offer potentially important advantages in terms of synthesis, conjugation, and reduced immunogenicity. The central hypothesis of the proposed studies is that aptamer-targeted siRNA inhibition of intracellular mediators in vaccine-induced CD8+ T cells will enhance their differentiation into long-lasting memory T cells and potentiate antitumor immunity that will be superior to pharmacological agents in terms of reduced toxicity, increased efficacy, and applicability to nondrugable intracellular targets. The proposed approach is supported by preliminary studies showing that 4-1BB aptamer-targeted raptor siRNA inhibition of mTORC1 function in activated CD8+ T cells led to the generation of a potent memory response and enhanced vaccine-induced protective immunity in tumor-bearing mice that was superior to that of rapamycin. The specific goal of the studies proposed in this application is to identify a best-i-class aptamer-siRNA conjugate to potentiate vaccine-induced protective immunity as determined in murine tumor models (Aims #1 and #2), that will guide the development of human conjugates capable of promoting the persistence of antigen- activated T cells in vitro (Aim #3). Successful accomplishment of the goals of the proposed studies will set the stage for clinical trials to potentiate vaccine-induced protective immunity in cancer patients using the agents developed in this proposal. Promoting memory differentiation by inhibition of intracellular mediators using siRNAs that are targeted to activated CD8+ T cells by conjugation to oligonucleotide aptamer ligands is arguably novel. The ability to target siRNAs to specific subsets of circulating immune or hematopoietic cells will provide a novel tool to manipulate the immune and hematopoietic systems for both investigational and therapeutic purposes.